Professor Babu's research group is
continuing the investigation of various aspects of chemical-mechanical
polishing (CMP) of metal and dielectric films and deposition and characterization
of silicon- containing diamondlike carbon films (DLC). Along with the
polishing of silicon dioxide films, the CMP research is focused on the
planarization of Cu and Ta films, using both alumina and silica abrasives
in different chemical environments. A recent addition has been the development
of very high selectivity novel ceria based slurries for STI planarization.

The changes in the film surface hardness in the presence
of different oxidizing chemicals are being measured using nanoindentation.
These changes have a strong influence on the quality of the planarized
film surface and the choice of an abrasive. Measurements, both in air
and in the chemical environments of interest to CMP, are being performed.
Electrochemical measurements, both in situ and ex situ, are providing
valuable insights into material removal mechanisms. Ionic strength and
pH have been shown to play an important role in determining removal rates
of Cu and Ta films in different polishing environments. Polishing of Cu
and Ta with silica abrasives of different surface areas suggests that
the surface hydroxyl groups play an important role in material removal.
Cu and Ta removal rates increase with increasing surface area of the silica
abrasives. Lowering the surface hydroxyl concentration by partially replacing
them with methyl groups lowered the removal rates, with the effect being
more pronounced for Ta than for Cu. In one set of experiments, it was
found that about 75 % of the removed Ta is attached to the silica particles
while only about 44% of removed Cu is. In contrast, when alumina abrasives
are used, about 88% of the removed Cu is present in solution. These experiments
are being done in collaboration with Professor Li's group.

The effects of abrasive shape, size and morphology in CMP
are being investigated in collaboration with Professor Matijevic¢.
With support from SRC, well-defined dispersions using monodispersed spherical
silica particles, silica particles coated with aluminum (hydrous) oxide,
ellipsoidal particles of different anisometries coated with silica, and
silica particles coated with ceria are being prepared and will be evaluated
as abrasives in CMP.

A Westech 372, donated by Intel, has been installed and
is providing a sorely needed extension to CAMP's planarization capabilities
to be further extended soon by a 676 Orbital tool provided by Speedfam/IPEC.
Also, IBM has donated two Westech 4100 polisher/brush cleaner systems.

Current research sponsors include New York State Energy
Research and Development Authority (NYSERDA), SRC/Intel, Grace Davison,
St. Gobain, PPG, Nyacol, Rodel, and Kodak, Inc. Professor Babu's research
group now consists of five Ph.D. and three M.S. students.

Laser-Based
Particle Removal

Professor Cetin Cetinkaya's ongoing
experimental work includes laser-based particle removal, ultrasonic methods
for particle characterization and air-coupled ultrasonic evaluation. He
is also interested in linear and nonlinear elastic and thermoelastic wave
propagation and its applications in non-contact submicron and nanoparticle
removal, mechanical particle-surface bond characterization and ultrasonic
testing and evaluation.

Nanoparticle
Removal in Front End of the Line Cleaning

With the International Technology Roadmap for Semiconductors
decreasing particle removal requirements from 125 nm (0.3-0.75 per cm2)
in 1997 to 25 nm (0.01 - 0.15 per cm2) in 2011, an era of the most challenging
cleaning applications in semiconductor manufacturing is upon us. Professor
Ahmed Busnaina and his group are addressing this problem.
In order to meet these removal requirements, there is a need to understand
the particle removal mechanisms and their limitations. See Figure 4.

Professor Busnainaand
his group have been investigating the effect of decreasing particle size
down to the nanoscale and its effect on the practical use of present techniques
in the future. The study shows that the removal of nanosize particles
(10-100 nm) can be best accomplished using acoustic streaming at frequencies
larger than 1 MHz. The theory shows that the removal of silica particles
in the nano-size (10-100 nm) range is achievable. It is also shown that
megasonic wave induced acoustic streaming is essential to the removal
of submicron particles. As the frequency increases, the acoustic boundary
layer thickness decreases and the streaming velocity increases thereby
increasing the drag force and consequently the removal moment. The results
show that the removal moment has to overcome the adhesion moment. The
force required to remove a particle by rolling is less than that required
by sliding or lifting. The experimental results also show that complete
removal down to 100 nm particles is achievable using a single wafer non-contact
cleaning process with DI water only.